Murine typhoid is a naturally occurring disease in mice which is caused by Salmonella typhimurium. This experimental model represents a good system with which to study the interactions between host and parasite and is especially important since the pathogenesis of this disease is similar to typhoid fever in man. Although the role of lymphocytes in the regulation of this disease has not been studied extensively, previous studies suggested that the murine immune response to S. typhimurium was primarily regulated by T cells and macrophages. However, recent observations suggest that B cells also play an important role in resistance. Since the characteristics of salmonella-specific B cells and their antibody products have not been critically analyzed, it is the specific aim of this proposal to study the function and specificity of B lymphocytes in the immune response to murine typhoid. First, a modification of the splenic fragment culture system will be utilized to assess the antibody responses of primary and secondary salmonella-specific B cells from normal and antibody-defective (xid) mice. This experimental system permits the isolation and stimulation of individual salmonella-specific B cells. Therefore, the characteristics of individual salmonella specific B-cell clones can be analyzed and compared. These studies will include: 1) heavy chain class analyses of the antibody produced by individual salmonella-specific B cells; 2) isoelectric focusing analysis of these antibody clones; 3) determination of the frequency of salmonella-specific B cells in salmonella resistant and susceptible mice. Second, the role of specific anti-salmonella antibodies in protective immunity will be determined. Previous studies have shown that passive transfer of whole immune mouse serum will increase the resistance of xid mice to murine typhoid. In the studies proposed herein, hybridoma antibodies which are specific for a given Salmonella cell surface antigen will be generated and their capacity to protect salmonella-susceptible (xid) mice will be analyzed. These studies should provide information which is critical for the development of effective and long lasting vaccines for typhoid and should also provide an experimental approach for the analysis of the humoral immune responses directed against other infectious disease agents.